In the field of semiconductor processing in recent years, it has become more and more necessary to achieve miniaturization of circuit patterns, particularly due to the trend toward higher integration densities of LSIs (large scale integrated circuits). As a result, there has been an increasing demand for a technology for reducing the line width of wiring patterns constituting the circuits and for miniaturizing contact hole patterns formed for interlayer wiring in the structure of cells. Accordingly, in the manufacture of a photomask on which a circuit pattern is written and which is used in photolithography for forming the wiring pattern or contact hole pattern, also, a technology by which circuit patterns can be written more finely and accurately is being requested in response to the progress of the miniaturization.
For forming a more accurate photomask pattern on a photomask substrate, first, it is necessary to form a high-accuracy resist pattern on the photomask blank. In photolithography at the time of actual processing of a semiconductor substrate, reduction projection is performed. Therefore, the size of the photomask pattern is about four times the size of the pattern actually needed. However, the accuracy requirement is not loosened that much. Rather, the accuracy required of a photomask used as an original is higher than the accuracy required of a pattern obtained after exposure.
Further, in the lithography carried out at present, the sizes of the circuit patterns to be written are considerably smaller than the wavelength of the light used. If use is made of a photomask pattern formed by simply magnifying the circuit shape by a factor of four, therefore, a shape in exact conformity to the photomask pattern cannot be transferred to a resist film, due to the influences of light interference generated in actual photolithography, etc. In order to reduce these influences, it may in some cases be necessary for the photomask pattern to be processed into a shape which is more complicated than the actual circuit pattern (a shape which is obtained by application of the so-called OPC (Optical Proximity Effect Correction) or the like). Therefore, in the lithographic technology for obtaining a photomask pattern, also, a processing method for yet higher accuracy is being requested at present. The performance of lithography is sometimes represented by the limit resolution. As the resolution limit, a limit resolution accuracy comparable to the resolution limit necessary for photolithography used in a semiconductor processing step using a photomask is demanded for the lithographic technology employed in a photomask processing step.
Formation of a photomask pattern is normally conducted by forming a photoresist film on a photomask blank having a light-shielding film on a transparent substrate, writing a pattern by use of an electron beam, obtaining a resist pattern through development, and then etching the light-shielding film while using the resulting resist pattern as an etching mask, to thereby process the light-shielding film into a light-shielding pattern. In miniaturizing the light-shielding pattern, if it is attempted to carry out the processing while maintaining the thickness of the resist film at the same level as that before miniaturization, the ratio of the film thickness to the pattern, namely, the so-called aspect ratio would become higher. This would cause deterioration of resist pattern shape, making it impossible to achieve satisfactory pattern transfer, or may result in collapse or peeling of the resist pattern. Accordingly, it is necessary to reduce the resist film thickness as miniaturization progresses.
On the other hand, when used as a light-shielding film material, silicon-based materials such as a material containing silicon or a material containing silicon and a transition metal are excellent in light-shielding characteristic for exposure light with a wavelength of 200 nm or below, can be processed by fluorine-based dry etching less liable to damage the resist pattern, and can be processed at higher accuracy, as compared with chromium-based materials which have hitherto been used (JP-A 2007-241065). In addition, it has been found that, when this technology is combined with a technology of using a hard mask formed from a chromium-based material in order to achieve processing with a higher accuracy, it is possible to carry out the processing with a higher precision (JP-A 2007-241060). Accordingly, light-shielding films composed of a silicon-based material film are considered to be promising as a material for a next-generation light-shielding film.
The following references relate to the invention.
JP-A 2007-241065; JP-A 2007-241060; JP-A 2006-146152;
JP-A S63-85553; JP-A 2001-27799; JP-A 2006-078807